Process for making pitch impregnated articles

ABSTRACT

Disclosed is a pitch impregnant composition comprising coal tar pitch, oxidized, or unoxidized petroleum pitch with stearic acid, and particulated metallic pigments including copper, aluminum, steel, silver, iron, tin, nickel and zinc metals and copper-zinc alloys. The process comprises forcing the molten impregnant composition into the surface of the porous article preferably by imposing pressure on the impregnant composition while the article to be treated is immersed therein. Articles so treated exhibit a metallic surface appearance.

NATURE OF INVENTION

This invention relates to bituminous impregnant compositions (particularly those containing either coal tar pitch, oxidized or unoxidized petroleum pitches) used for impregnating porous articles. More particularly this invention is concerned with those pitch impregnant compositions used to impregnate fibrous thick-walled paper tubes to form pitch-impregnated pipe for low pressure commercial use.

PRIOR ART

Pitch-impregnated fiber pipe is a well-known article of commerce. In general, the walls of this pipe are of a porous fibrous structure with pitch filling most of the void space in the structure. Ordinarily the pipe is made by forming thick-walled tubes from a paper slurry, drying the tubes, immersing them in the molten pitch impregnant, applying a vacuum to the pitch and tubes, and then admitting atmospheric pressure to the system. The pipe produced has sufficient rigidity and resistance to moisture that it finds many underground uses, such as for drain pipe, where internal pressures in the pipes are not excessively high.

More recently pitch-impregnated fiber pipe having a metallic colored, metallized or "aluminized" surface has been available commercially. This pipe is manufactured in the manner summarized above except that the molten pitch impregnant has suspended in it a metal pigment, which plates out or "leafs" on to the exterior surface of the pipe during the impregnation process. This metallized or aluminized pipe, as well as being aesthetically pleasing, displays improved resistance to water penetration in comparison to pitch-impregnated pipe not having a metallized surface.

Heretofore best results have been achieved using a pitch impregnant composition made up of unoxidized (or thermal) petroleum pitch, and a "leafing" aluminum pigment. However, using non-leafing aluminum pigments in thermal petroleum pitch, or using the oxidized petroleum pitches or coal tar pitches with leafing or non-leafing aluminum pigment, or using metallic pigments other than leafing aluminum with any of the coal tar, oxidized or unoxidized petroleum pitches does not always result in a pipe whose wall surfaces have a metallic color.

OBJECT OF THE INVENTION

An object of this invention is to provide an improved bituminous composition for impregnating porous objects and a process for impregnating the surface of porous objects with said composition to provide an object having a metallic colored surface the metal color being derived from metal pigments other than leafing aluminum.

Another object of this invention is to enable the use of coal tar pitches and oxidized petroleum pitches in combination with metal pigments to provide a suitable impregnant composition.

SUMMARY OF THE INVENTION

Briefly stated, this invention comprises in one of its aspects an impregnant composition for impregnating porous objects (for example, porous tubes in the manufacture of pitch-impregnated fiber pipes) comprising

a. a bituminous material

b. a metallic pigment, and

c. stearic acid

In another aspect, this invention comprises a process whereby a porous object is at least partially impregnated with the foregoing impregnant composition thereby providing a bitminous-impregnated article having a metallic colored surface.

Another aspect of this invention is the porous article itself, at least partially impregnated with an impregnant-composition comprising a bituminous material, a metal pigment, and stearic acid.

DETAILED DESCRIPTION OF THE INVENTION The Impregnant Composition

The impregnant composition of this invention comprises a bituminous material, a metal pigment, and stearic acid.

The primary bituminous materials for use in this composition are coal tar pitch, unoxidized or thermal petroleum pitch and oxidized petroleum pitch. Coal tar pitch ordinarily has a softening point of between about 145°F and 165°F. Oxidized petroleum pitch is familiar to those skilled in the art, and is derived by air blowing certain petroleum refinery flow streams to obtain a desired pitch product. The softening points of the oxidized petroleum pitches ordinarily is between about 155°F and about 175°F.

Unoxidized petroleum pitch can be further characterized as unmodified thermal petroleum pitch. These pitches remain rigid at temperatures closely approaching their melting points. The preferred procedure for preparing the unoxidized petroleum pitch uses as starting material, a clarified slurry oil or cycle oil from which substantially all paraffins have been removed in fluid catalytic cracking. Where the fluid catalytic cracking is not sufficiently severe to remove substantially all paraffins from the slurry oil or cycle from the slurry oil or cycle oil, they may be extracted with furfural. In either case, the resultant starting material is a highly aromatic oil boiling at about 700° to 850°F. This oil is thermally cracked at elevated temperatures and pressures for a time sufficient to produce a thermally cracked petroleum pitch with a softening point of about 100°F to about 260°F. The manufacture of unoxidized petroleum pitches is described in U.S. Pat. No. 2,768,119 and 3,140,248. Table I presents comparative properties of four unoxidized petroleum pitches (A, B, C and D) and an oxidized pitch (E).

                                      TABLE I                                      __________________________________________________________________________     Test           Test Method                                                                            Pitch A                                                                              Pitch B                                                                              Pitch C                                                                              Pitch D                                                                              Pitch E                         __________________________________________________________________________     Softening Point, °F., R&B                                                              ASTM D-2398                                                                            173   174   168.5 166   174                             Density, G/cc  Mettler 1.192 1.205 1.160 1.178 1.186                           Mod. Con. Carbon Wt.%                                                                         ASTM D-2416                                                                            37.8  43.8  39.6  36.9  37.1                            Flash, COC, °F.                                                                        ASTM D-92                                                                              540   495   545   535   480                             Pen. 100/5/77  ASTM D-5                                                                               0     0     0     0     0                               Pen. 200/60/115                                                                               ASTM D-5                                                                               128   47    208   --    123                             Pen. 50/60/15  ASTM D-5                                                                               40    37    68    --    48                              Sulfur, Wt.%   ASTM D-1552                                                                            2.73  1.47  2.01  0.95  1.69                            Benzene Ins., Wt.%                                                                            ASTM D-2317                                                                            0.80  11.7  1.9   2.3   8.1                             Quinoline Insol., Wt.%                                                                        ASTM D-2318                                                                            0.11  (1)   Nil   Nil   Nil                             Viscosity, CPS 350                                                                            Brookfield                                                                             40    70    45    32    70                              No. 2 Spindle, 325                                                                            Brookfield                                                                             60    110   82.5  65    125                              30 RPM) 300   Brookfield                                                                             140   230   165   135   240                             __________________________________________________________________________      (1)Quantity of solids content too great to permit filtering              

The amount of metal powder or paste pigment mixed with the bituminous material will, of course, vary. The minimum amount will be that required to achieve a desired surface color of the finished product. The maximum amount will be determined by the economics of the process and the possibility of uneven penetration by the molten bituminous material if too much filterable metal pigment is suspended in the pitch impregnant. Ranges of 0.1 to 1.4 or preferably 0.3 to 0.7 parts by weight of metal pigment per 100 parts of bituminous material can be used. These values for the metal pigment concentration are based on pigment alone and do not include any additional solvents or stabilizing materials which may be present. The ranges given are not restrictive. Less or greater concentrations of metal pigment can be added.

As to specific metal pigments applicable to this invention aluminum, silver, stainless steel, iron, tin, nickel, copper and zinc pigments, as well as copper-zinc alloys, have all been found usable in the composition and method of this invention. Any metallic powder produced in a ball mill or hammer mill where stearic acid is used as a lubricant in the milling process can be used. It is believed the milling process causes the stearate salt of the metal to be formed on the surfaces of the pigment particles.

As to the stearic acid used, it is preferred to add between about 4 and 30 parts by weight per 100 parts of metal pigment. This will depend upon the type of pigment. The commercial grades of stearic acid commonly available are suitable for use.

In all of the following examples the metal pigment had been milled with stearic acid during its manufacture.

EXAMPLES 1 - 9

Table II summarizes data on impregnant compositions in which approximately one part by weight of the metal flake pigment indicated was mixed with 100 parts by weight of molten bituminous material. In runs 2 - 9 inclusive between 2 and 3 parts by weight of stearic acid per 100 weights of metal pigment was included. In Run No. 1 no stearic acid was added. In each run the molten mixture was poured into a small puddle on a rigid surface and cooled to room temperature whereupon each sample solidified to a flat mass having a smooth surface. The appearance of each surface was then examined for its metallic color. In Runs 2 - 9, each sample exhibited a metallic color. Stated in another way, the metallic pigment in each sample "leafed" resulting in the desired metal color.

The term "leafing" is well known to those in the art and is defined in Federal Test Method Standard No. 141. Leafing refers to the fact that certain metallic pigments occur in the form of thin flakes. When such pigments are mixed with a vehicle and applied as a paint film, the thin flakes float and concentrate at the surface of the paint film where they overlay each other.

Although the compositions of Runs 2 - 9 were not tested by impregnating a porous article (such as the porous fibrous paper cylinders used in the manufacture of pitch-impregnated fiber pipe) the test results show the impregnant compositions of Runs 2 - 9 would yield a metallized or metallic colored surface, if used in the impregnation process hereinafter described.

                                      TABLE II                                     __________________________________________________________________________     Metallized Pitch Impregnants                                                   (Approx. 1% Metal Flake and 0.2 to 0.3% Stearic Acid Added to Each             Blend).sup.1                                                                   Except Item 1                                                                              Desig-      Metallic Flake                                                                          Type of                                       Run                                                                               Metallic Flake                                                                          nation                                                                               Lot No.                                                                              Manufacturer                                                                            Pitch      Comments                           __________________________________________________________________________     1  Aluminum 3A    --    Reynolds Oxidized   Trace of Leafing                      Paste                         Petroleum, SP 170                                                                         (No stearic acid added)            2  Aluminum 3A    --    Reynolds Oxidized   Leafing Excellent                     Paste                         Petroleum, SP 170                                                                         (Stearic acid added)               3  Silver   MD 750                                                                               L-4512-S                                                                             Alcan    Thermal    Leafing Good                                         11/27/72       Petroleum, SP 170                             4  Stainless                                                                               MD 756                                                                                3181-S                                                                              Alcan    Thermal    Leafing Good                          Steel Flake    11/27/72       Petroleum, SP 170                             5  Iron     MD 750                                                                                4214-S                                                                              Alcan    Thermal    Leafing Excellent                     Flake          11/27/72       Petroleum, SP 170                                                                         (Not as reflective as                                                          aluminum)                          6  Stainless                                                                               MD 750                                                                                3958-S                                                                              Alcan    Thermal    Leafing Excellent                     Steel          11/27/72       Petroleum, SP 170                                                                         (Not as reflective as                                                          aluminum)                          7  Tin      MD 750                                                                                4453-S                                                                              Alcan    Thermal    Leafing Good                          Flake          11/27/72       Petroleum, SP 170                             8  Nickel   MD 756                                                                                4099-S                                                                              Alcan    Thermal    Leafing Fair                          Flake          11/27/72       Petroleum, SP 170                             9  Zinc     XMR 125                                                                               3003-S                                                                              Alcan    Thermal    Leafing Excellent                     Flake          11/27/72       Petroleum, SP 170                                                                         (Very similar to                   __________________________________________________________________________                                                 aluminum)                           .sup.1 Flake and Stearic acid weight per cent calculated on weight of          pitch component.                                                               .sup.2 The term "Reynolds" indicates Reynolds Metals Company, Richmond,        Virginia, and the term "Alcan" denotes Alcan Aluminum Corporation,             Elizabeth, New Jersey.                                                   

EXAMPLE 10

In a test similar to that described above a gold-colored pigment comprising approximately 80 percent copper and 20 percent zinc, trade-named MD 150 Rich Gold Powder and sold commercially by Alcan was mixed in a ratio of 1 part of pigment by weight to 100 parts by weight of an unoxidized petroleum pitch having a softening point of 170°F. This mixture when poured in a molten condition onto a flat surface and cooled did not exhibit a leafing effect. This run was repeated but 20 parts by weight of stearic acid per hundred parts of metal pigment were added. When a portion of the molten mixture was puddled onto a flat surface and cooled, the surface exhibited a gold color. The copper-zinc pigment had leafed. In a similar test using a 100 percent copper pigment, trade-named MD150 copper powder and marketed by Alcan, leafing also occurred in the presence of added stearic acid.

EXAMPLE 11

A section of dry paper tubing was impregnated by immersing the tube in a molten bath of unoxidized petroleum pitch having a softening point of 170°F containing 1 part by weight of the copper-zinc pigment of Example 10 per 100 parts by weight of pitch and 20 percent by weight of stearic acid per 100 parts by weight of metal pigment. The dry paper tubing was of the type which is now used in the commercial manufacture of pitch impregnated fiber pipe. The manufacture of these tubes is well known in the prior art. Ordinarily a pulp slurry of a fibrous material first is made. Newsprint is a common material for the pulp slurry, although other materials such as chemical pulp and asbestos fibers may also be added. A wet web of interfelted cellulose fiber is deposited from the slurry onto a felt roll. Subsequently the web is wound onto a mandrel to form a tube of a desired wall thickness. Each wet tube on a supporting mandrel is then passed through a drying oven, and the mandrel subsequently is removed. The result is a dry paper tube of a desired wall thickness. The tube in this example was impregnated by first subjecting the molten mixture of unoxidized pitch, copper-zinc pigment and stearic acid to a vacuum and then imposing atmospheric pressure on the system. The tube was then removed from the molten bath and cooled. The pitch impregnated pipe had a gold metallic colored surface.

EXAMPLE 12

As to the manner of impregnating an article with impregnant containing bituminous material, metal pigment and stearic acid, any of the methods presently used in the art can be employed. These include simple soaking in an open tank over a period of time, pressure saturation, vacuum saturation, and combined pressure and vacuum saturation.

As noted previously, a more specific embodiment of this invention is the manufacture of bituminous impregnated fiber pipe in which fibrous tubes are impregnated with molten pitch containing suspended metal pigment and stearic acid therein. In this particular embodiment the fibrous tubes to be impregnated are of the kind presently used in conventional fiber pipe manufacturing. As discussed previously, they are made by winding a wet web of cellulose pulp on a mandrel to the desired wall thickness and then drying the tube either before or after it had been removed from the mandrel. The technique of forming these dried paper tubes is well known in the art and is discussed briefly in U.S. Pat. Nos. 1,803,409; 1,854,230; and 1,860,674.

The impregnant composition can be prepared in several ways. If the metal pigment has been supplied in paste form with a liquid carrier, it along with the desired amount of stearic acid, can be manually added to the mass of molten pitch and the mixture agitated by stirring or circulation. For impregnating purposes, the temperature of the metal pigment, stearic acid-pitch mixture can be in the range of 270° to 375°F. This temperature will, of course, vary depending upon the properties of the particular pitch.

The step of impregnating the dry paper tubes can be performed in any manner which will force the pitch into the pores and interstices of the paper tubes. A preferred method is one wherein the paper tubes are placed in a pressure vessel and subjected to a vacuum for a number of minutes. The molten impregnant mixture is then pumped into the pressure vessel until the tubes are submerged. The molten mixture is circulated for a period of minutes to insure an even distribution of all components of the impregnant. The pressure in the vessel is then raised to atmospheric pressure thereby forcing the pitch into the pore spaces of the paper tubes. The remaining molten impregnant mixture is then drained from the vessel, and the tubes are withdrawn and quenched.

It is not completely understood as to what phenomenon occurs. There is, of course, a filtering action in which the suspended pigment is retained in a film of pitch on the surfaces of the paper tubes.

EXAMPLE 13

The addition of stearic acid to mixtures of thermal (unoxidized) petroleum pitch and leafing aluminum pigment in the manufacture of pitch-impregnated fiber pipe having a metallic colored or "aluminized" surface provides an added benefit. Aluminized pitch impregnated pipe can be manufactured using thermal petroleum pitch and leafing aluminum pigment alone; however, the addition of stearic acid imparts a better color to the pipe and enables the use of less aluminum pigment than would otherwise be necessary.

It has been found that an impregnant composition made up in the ratio of 1 part of aluminum pigment to 100 parts by weight of thermal petroleum pitch would produce a pitch impregnated fiber pipe having a suitable metallic colored surface; however, if stearic acid is added in the ratio of about 8 to 10 parts by weight of acid to 100 parts by weight of pigment as little as 0.85 parts by weight of an aluminum pigment trade-named Reynold's 3A paste per 100 parts of pitch and as little 0.75 parts by weight of an aluminum pigment trade-named Alcan MD 462 paste per 100 parts by weight of pitch are required to produce a pipe having an acceptable metallic colored surface.

Although the foregoing description has been directed primarily to processes and compositions relating to the manufacture of bituminous-impregnated fiber pipe it is to be understood this invention is also applicable to the manufacture of other articles wherein it is desired to produce an article having a surface at least partially impregnated with bituminous or pitch material and having a metallic colored surface. Such articles include building board, ceramic bodies, and roofing felt. The article to be treated must be sufficiently permeable to enable at least partial penetration of the impregnant composition into the surface of the article. The article must also be stable at the temperature of impregnation. 

I claim:
 1. In a process for manufacturing an impregnated fiber pipe wherein;a. a porous tubular body is formed; b. the tubular body is immersed in a liquid mixture of (1) a particulated metallic pigment previously milled in the presence of stearic acid, and (2) molten pitch selected from the group consiting of coal tar pitch, oxidized petroleum pitch, unoxidized petroleum pitch and mixtures thereof at a temperature of about 270°F to about 375°F., and c. said liquid mixture is forced into interstices in said tubular form; the improvement comprising: d. prior to immersing said tubular body in said mixture dispersing between about 4 and about 30 parts by weight of additional stearic acid per 100 parts of metallic pigment in said mixture.
 2. A process for manufacturing a pitch-impregnated fiber pipe comprising;a. forming a tubular body of interfelted fibrous material; b. immersing said tubular body of (a) in a liquid impregnant at a temperature of about 270°F. to about 375°F., said liquid impregnant comprising unoxidized-petroleum pitch, suspended aluminum particles previously milled in the presence of stearic acid, and between about 4 and about 30 parts by weight of additional stearic acid per 100 parts of aluminum; and c. forcing said liquid impregnant of (b) into the pore spaces and interstices of said tubular body, thereby depositing a film of aluminum particles on the surface of said impregnated tubular body.
 3. The process of claim 2 wherein the concentration of aluminum particles in said liquid impregnant is at least about 0.75 parts by weight per 100 parts by weight of pitch.
 4. The process of claim 2 wherein said tubular body of (a) comprises interfelted cellulose fibers.
 5. A process for manufacturing a pitch-impregnated fiber pipe comprising;a. forming a tubular body of interfelted fibrous material; b. immersing said tubular body of (a) in a liquid impregnant at a temperature of about 270°F. to about 375°F., said liquid impregnant comprising unoxidized-petroleum pitch, suspended metal pigment selected from the group consisting of silver, stainless steel, iron, tin, nickel, copper, zinc and alloys of copper and zinc, said metal pigment being previously milled in the presence of stearic acid, and between about 4 and about 30 parts by weight of additional stearic acid per 100 parts of metal pigment; and c. forcing said liquid impregnant of (b) into the pore spaces and interstices of said tubular body, thereby depositing a film of metal pigment on the surface of said impregnated tubular body. 